This is what UX has decided makes sense, and will be much less disruptive than dimming out all favicons on session restore. When we're ready the default value of "browser.tabs.fadeOutExplicitlyUnloadedTabs" will be true, and the default value of "browser.tabs.fadeOutUnloadedTabs" will remain false. Differential Revision: https://phabricator.services.mozilla.com/D241481